1. Field of the Invention
The invention relates to a method of manufacturing a laminated wafer by a high temperature laminating method.
2. Description of the Related Art
There is conventionally proposed Silicon on Insulator [SOI] wafers called a Silicon on Quartz (SOQ) wafer, a Silicon on Glass (SOG) wafer and a Silicon on Sapphire (SOS) wafer in which a donor wafer made of silicon is bonded to a handle wafer made of e.g. quartz, glass and sapphire. The insulation property and the transparent property of the handle wafer may expand the application of the SOI wafers to e.g. a projector and a high-frequency device. In particular, the SOS wafer has a thermal conductivity about 30 times as high as that of quartz, it may be applied to devices that would generate large amount of heat.
A conventional SOI manufacturing technique as to bonding is mainly categorized into two methods. One method is a SOITEC method. A silicon wafer (donor wafer), which has been subjected to hydrogen-ion-implantation in advance, is bonded with a wafer (handle wafer) acting as a support substrate at a room temperature. The laminated wafer are subjected to heat treatment at a high temperature (about 500° C.), and then delaminated at an ion implantation interface by generating a lot of minute bubbles called micro cavities at the ion implantation interface so as to transfer a silicon film onto the handle wafer.
The other method is called a SiGen method. A wafer, which has been subjected to the hydrogen ion implantation in advance, is bonded with a handle wafer after the surfaces of both the silicon wafer and the handle wafer to be bonded are activated by a plasma treatment, and thereafter the laminated wafer is mechanically delaminated at the hydrogen-ion-implantation interface.
Since the SOITEC method comprises the step of a high temperature heat treatment after the laminating step, when silicon is bonded to a handle wafer such as quartz and sapphire, the handle wafer may be cracked in the step of heat treatment due to a large difference in thermal expansion coefficient. Further, in the SiGen method, although both the wafers have a high coupling strength due to the surface activation treatment in comparison with the SOITEC method when the wafers are bonded, they must be subjected to a heat treatment at 200° C. or higher. As a result, the laminated wafer may be broken due to the difference in thermal expansion coefficient between the wafers or an untransferred portion may be observed in a resultant silicon film.